SEPTEMBER,  1916  BULLETIN  380 

CORNELL  UNIVERSITY 
AGRICULTURAL   EXPERIMENT   STATION 


THE  HARD  ROT  DISEASE  OF  GLADIOLUS 


L.  M.  MASSEY 


ITHACA,  NEW  YORK 
PUBLISHED  BY  THE  UNIVERSITY 


SI??  1.  M.  Hill  ICthrarg 


Hortfj  (Carolina  &tate  Initirrflitg 

S3308 

G55 

M3 


•:-'-:  i!¥ 


THIS  BOOR  IS  DUE  ON  THE  DATE 
INDICATED  BELOW  AND  IS  SUB- 
JECT TO  AN  OVERDUE  FINE  AS 
POSTED  AT  THE  CIRCULATION 
DESK. 


SEPTEMBER,   191«  BULLETIN  380 

CORNELL  UNIVERSITY 
AGRICULTURAL  EXPERIMENT  STATION 


THE  HARD  ROT  DISEASE  OF  GLADIOLUS 


L.  M.  MASSEY 


ITHACA,  NEW  YORK 
PUBLISHED  BY  THE  UNIVERSITY 


D.  H.  HILL  LIBRARY 
N.  C.  STATE  UNIVERSITY 


CORNELL  UNIVERSITY 
AGRICULTURAL  EXPERIMENT  STATION 

Experimenting  Staff 

ALBERT  R.  MANN,  B.S.A.,  A.M.,  Acting  Director. 
HENRY  H.  WING,  M.S.  in  Agr.,  Animal  Husbandry-. 
T.  LYTTLETON  LYON,  Ph.D.,  Soil  Technology. 
JOHN  L.  STONE,  B.Agr.,  Farm  Practice. 
JAMES  E.  RICE,  B.S.A.,  Poultry  Husbandry. 
GEORGE  W.  CAVANAUGH,  B.S.,  Agricultural  Chemistry. 
HERBERT  H.  WHETZEL,  M.A.,  Plant  Pathology. 
ELMER  O.  FIPPIN,  B.S.A.,  Soil  Te?hnology. 
G.  F.  WARREN,  Ph.D.,  Farm  Management. 
WILLIAM  A.  STOCKING,  Jr.,  M.S.A.,  Dairy  Industry. 
WILFORD  M.  WILSON,  M.D.,  Meteorology. 
RALPH  S.  HOSMER,  B.A.S.,  M.F.,  Forestry. 
JAMES  G.  NEEDHAM,  Ph.D.,  Entomology  and  Limnology. 
ROLLINS  A.  EMERSON,  D.Sc,  Plant  Breeding. 
HARRY  H.  LOVE,  Ph.D.,  Plant  Breeding. 
ARTHUR  W.  GILBERT,  Ph.D.,  Plant  Breeding. 
DONALD  REDDICK,  Ph.D.,  Plant  Pathology. 
EDWARD  G.  MONTGOMERY,  M.A.,  Farm  Crops. 
WILLIAM  A.  RILEY,  Ph.D.,  Entomology. 
MERRITT  W.  HARPER,  M.S.,  Animal  Husbandry. 
JAMES  A.  BIZZELL,  Ph.D.,  Soil  Technology. 
GLENN  W.  HERRICK.  B.S.A.,  Economic  Entomology. 
HOWARD  W.  RILEY,  M.E.,  Farm  Mechanics. 
CYRUS  R.  CROSBY,  A.B.,  Entomology. 
HAROLD  E.  ROSS,  M.S.A.,  Dairy  Industry. 
KARL  McK.  WIEGAND,  Ph.D.,  Botany. 
EDWARD  A.  WHITE,  B.S.,  Floriculture. 
WILLIAM  H.  CHANDLER,  Ph.D.,  Pomology. 
ELMER  S.  SAVAGE,  M.S.A.,  Ph.D.,  Animal  Husbandry. 
LEWIS  KNUDSON,  Ph.D.,  Plant  Physiology. 
KENNETH  C.  LIVERMORE,  Ph.D.,  Farm  Management. 
ALVIN  C.  BEAL,  Ph.D.,  Floriculture. 
MORTIER  F.  BARRUS,  Ph.D.,  Plant  Pathology. 
CLYDE  H.  MYERS,  M.S.,  Ph.D.,  Plant  Breeding. 
GEORGE  W.  TAILBY,  Jr.,  B.S.A.,  Superintendent  of  Livestock. 
EDWARD  S.  GUTHRIE,  M.S.  in  Agr.,  Ph.D.,  Dairy  Industry. 
JAMES  C.  BRADLEY,  Ph.D.,  Entomology. 
PAUL  WORK,  B.S.,  A.B.,  Vegetable  Gardening. 
JOHN  BENTLEY,  Jr.,  B.S.,  M.F.,  Forestry. 
EARL  W.  BENJAMIN,  Ph.D.,  Poultry  Husbandry. 
EMMONS  W.  LELAND,  B.S.A.,  Soil  Technology. 
CHARLES  T.  GREGORY,  Ph.D.,  Plant  Pathology. 
WALTER  W.  FISK,  M.S.  in  Agr.,  Dairy  Industry. 
ARTHUR  L.  THOMPSON,  Ph.D.,  Farm  Management. 
LEX  R.  HESLER,  A.B.,  Ph.D.,  Plant  Pathology. 
ROBERT  MATHESON,  Ph.D.,  Entomology. 
MORTIMER  D.  LEONARD,  B.S.,  Entomology. 
FRANK  E.  RICE,  Ph.D.,  Agricultural  Chemistry. 
VERN  B.  STEWART,  Ph.D.,  Plant  Pathology. 

IVAN  C.JAGGER,  M.S.  in  Agr.,  Plant  Pathology  fin  cooperation  with  Rochester  University). 
CHARLES  H.  HADLEY,  Jr.,  B.S.,  Entomology. 
DANIEL  S.  FOX,  B.S.,  Farm  Management. 
WILLIAM  I.  MYERS,  B.S.,  Farm  Management. 
LEW  E.  HARVEY,  B.S.,  Farm  Management. 
LEONARD  A.  MAYNARD,  A.B.,  Ph.D.,  Animal  Husbandry. 
LOUIS  M.  MASSEY,  Ph.D.,  Plant  Pathology. 
BRISTOW  ADAMS,  B.A.,  Editor. 
LELA  G.  GROSS,  Assistant  Editor. 
The  regular  bulletins  of  the  Station  are  sent  free  on  request  to  residents  of  New  York  State. 

I50 


CONTENTS 

PAGE 

The  host  plant 1 53 

Economic  importance  of  the  gladiolus  industry 153 

The  disease 153 

Economic  importance  of  the  disease 155 

Symptoms 156 

On  the  leaves 156 

On  the  eorms '. 156 

Etiology 157 

Life  history 158 

Pycnidia 158 

Mycelium 159 

Source  of  leaf  infection 159 

Source  of  corm  infection 161 

Longevity  of  the  organism  on  the  foliage  and  in  the  soil 162 

Pathogenicity 1 63 

Inoculation  experiments 163 

Pathological  histology 167 

Leaf 167 

Corm 168 

Cultural  characters  of  the  fungus 168 

Control 172 

Seedling  treatments 1 72 

Corm  treatments 173 

Healthy  corms  in  soil  free  from  the  pathogenes 1 73 

Healthy  corms  in  soil  known  to  harbor  the  pathogenes 175 

Diseased  corms  in  soil  free  from  the  pathogenes 175 

Spring  treatments 175 

Autumn  treatments 1 76 

Experiment  1.     Treatment  of  corms  with  formalin  and  corrosive 

sublimate  solutions 176 

Experiment  2.     Formaldehyde  gas  as  a  disinfectant 177 

Experiment  3.     Hot-water  and  hot-air  treatments  of  diseased 

corms 177 

Soil  treatments 178 

Experiment  1.     Chemicals 1 78 

Experiment  2.     Formalin  as  a  soil  disinfectant 179 

Experiment  3.     Formalin  as  a  soil  disinfectant 180 

Sanitation 1 80 

Bibliography 1 80 


151 


THE  HARD  ROT  DISEASE  OF  GLADIOLUS  * 

L.  M.  Massey 
THE  HOST  PLANT 
The  gladiolus  is  a  cormous,  summer-flowering  plant.  Pax  (i 889)2 
classifies  it  as  a  member  of  the  family  Iridaceae,  of  the  tribe  Ixioideae, 
subtribe  Gladioleae,  genus  Gladiolus.  The  species  of  Gladiolus  may  be 
grown  from  corms,  from  cormels  (the  grayish  to  black,  hard-shelled  bodies 
formed  on  underground  stems  at  the  base  of  the  new  corm) ,  or  from  seed. 
The  plants  are  indigenous  to  South  Africa,  where,  according  to  Crawford 
(Crawford  and  Van  Fleet,  1911:3),  about  fifty  species  have  been  dis- 
covered.    This  writer  states: 

It  is  also  a  native  of  middle  Africa,  central  and  southern  Europe,  Persia,  Caucasus, 
and  the  country  around  the  eastern  end  of  the  Mediterranean.  About  forty  additional 
species  have  been  found  in  these  localities,  and  one  in  Hampshire,  England.  These  have 
been  hybridized  and  crossed  until  they  are  so  mixed  that  it  is  impossible  for  the  ordinary 
grower  to  say  what  blood  may  have  entered  a  given  variety — nor  does  it  matter. 

ECONOMIC    IMPORTANCE    OF    THE    GLADIOLUS    INDUSTRY 

According  to  Hendrickson  (191 1),  there  are  from  four  hundred  to  five 
hundred  acres  in  the  United  States  devoted  to  gladioli,  the  annual  pro- 
duction of  corms  being  from  14,000,000  to  15,000,000  and  the  estimated 
value  of  the  crops  $250,000.  In  New  York  State,  besides  many  small 
growers  there  are  two  growers  each  having  over  one  hundred  acres  devoted 
entirely  to  the  cultivation  of  gladioli.  A  list  of  the  members  of  the 
American  Gladiolus  Society  which  appeared  in  19 14  in  the  Modern  Gladiolus 
Grower  (1:31-32)  contains  two  hundred  and  twenty  names,  of  which  but 
sixty-three  are  those  of  amateurs  and  twenty-eight  those  of  foreign  dealers 
and  growers.  The  output  of  these  growers  and  dealers  represents  only 
a  portion  of  the  total  output  of  the  United  States.  Almost  every  florist 
is  more  or  less  interested  in  the  production  of  corms  and  flowers  of  the 
gladiolus,  which  appears  to  be  increasing  in  popularity  as  a  cut  flower. 

THE  DISEASE 
The  name  hard  rot  was  given  to  the  corm  stage  of  the  disease  under 
consideration  by  Wallace  (1909:18),  who  makes  no  reference  to  a  leaf 
stage.     This  name  was  given  to  distinguish  the  disease  from  other  corm 

1  Also  presented  to  the  Faculty  of  the  Graduate  School  of  Cornell  University,  January,  1016,  as  a  major 
thesis  in  partial  fulfillment  of  the  requirements  for  the  degree  of  doctor  of  philosophy. 

Acknowledgment.  The  writer  wishes  to  express  his  indebtedness  to  Professors  Donald  Reddick  and 
H.  H.  Whetzel,  under  whose  immediate  direction  the  work  was  conducted,  for  helpful  criticisms  and 
suggestions. 

-  Dates  in  parenthesis  refer  to  bibliography,  page  180. 

153 


154  Bulletin  380 

diseases,  such  as  dry  rot  and  soft  rot,  with  which  both  Wallace  and 
Fitzpatrick 3  worked  prior  to  19 1 2 .  The  writer  took  up  the  investigation 
of  these  diseases  in  191 2  and  has  given  them  constant  study  since  that  time. 

Apparently  the  hard  rot  disease  of  gladiolus  exists  wherever  gladioli 
are  grown.  Specimens  have  been  received  from  many  of  the  largest 
growers  in  the  United  States.  Horticultural  publications  contain  many 
references  to  corm  rots,  and  no  doubt  much  of  this  injury  is  due  to  the 
hard  rot  disease.  Plants  growing  in  the  greenhouse  at  Cornell  University 
from  corms  received  from  Italy  by  A.  C.  Hottes  bore  the  leaf  stage  of  the 
disease.  The  writer  has  received  corms  affected  with  hard  rot  from 
Canada,  Germany,  and  Holland. 

Prillieux  and  Delacroix  (1894)  report  having  studied  a  disease  of  the 
gladiolus  in  which  the  tissue  was  deeply  corroded,  but  the  writer  is  unable 
to  determine  whether  or  not  it  is  the  same  disease  as  the  one  considered 
in  this  bulletin.  Unpublished  notes  placed  at  the  disposal  of  the  writer 
by  Professor  F.  C.  Stewart,  of  the  New  York  (Geneva)  Agricultural 
Experiment  Station,  mention  the  only  distinction  observed,  prior  to 
Wallace's  thesis  (1909),  between  two  types  of  rots.  Concerning  specimens 
of  diseased  corms  received  from  a  New  York  State  grower,  Professor 
Stewart  suggested  the  probability  that  they  were  affected  with  the  bac- 
terial disease  described  by  Prillieux  and  Delacroix,  since  he  was  unable 
to  locate  any  trace  of  fungous  hypha?  in  the  diseased  tissue.  Wallace 
(1909: 15)  was  of  the  opinion  that  the  corms  received  by  Professor  Stewart 
were  affected  with  the  hard  rot  disease. 

In  1874  Passerini  collected  specimens  of  the  leaf  stage  of  the  hard 
rot  disease,  which  he  contributed  to  exsiccatae  of  Rabenhorst's  Fungi 
Europaei. 

Saccardo  (1884)  reports  the  occurrence  of  the  leaf  stage,  of  the  disease 
on  Gladiolus  segetum  at  Parma,  Italy,  and  on  Gladiolus  gandavensis  at 
Coimbra,  Portugal.  Allescher  (1897),  in  addition  to  the  occurrence 
on  hosts  listed  by  Saccardo,  reports  the  disease  as  occurring  on  the  leaves 
of  Gladiolus  palustris  in  Silesia.  So  far  as  known  to  the  writer,  the  leaf 
stage  of  this  disease  has  never  been  reported  in  America.  A  "blight" 
is  frequently  mentioned  in  horticultural  publications,  but  the  descriptions 
of  the  injury  are  in  all  cases  so  indefinite  that  it  is  impossible  to  determine 
what  diseases  the  writers  had  under  observation.  Hicks  (1907:35)  and 
Childs  (1907)  write  of  gladiolus  leaf  blight,  but  there  is  nothing  in  their 
writings  sufficiently  definite  to  make  it  possible  to  determine  the  nature 
of  the  injury.  Halsted  (1 894-1 901)  reports  having  worked  on  gladiolus 
diseases,  but  leaves  the  reader  in  doubt  as  to  what  the  diseases  were. 


3  Unpublished  notes  of  Professor  H.  M.  Fitzpatrick,  of  Cornell  University,  covering  his  investigations 
of  gladiolus  diseases,  were  kindly  placed  at  the  disposal  of  the  writer. 


The  Hard  Rot  Disease  of  Gladiolus 


*55 


Undoubtedly  the  leaf  stage  of  the  hard  rot  disease  occurs  more  generally 
throughout  the  country  than  is  indicated  by  an  examination  of  literature. 
This  is  due  to  importation  of  stock  from  Europe  and  exchange  of  stock 
by  growers  in  this  country.  On  the  other  hand,  the  writer  has  observed 
specimens  of  the  disease  on  the  foliage  of  plants  grown  by  but  three  large 
growers. 

Foliage  affected  with  the  disease  was  first  observed  by  the  writer  in 
19 1 2  in  seedling  beds,  and  later  on  plants  grown  from  cormels.  Not 
until  the  season  of  19 15  did  the  writer  find  the  disease  on  the  foliage  of 
large  plants,  at  which  time  six  plants  of  flowering  size  were  observed  to  be 
affected.  In  many  cases  large  flowering  plants  of  different  varieties 
have  been  observed  growing  in  seed  beds  or  among  plants  from  cormels, 
all  of  which  were  badly  diseased  and  yet  the  large  plants  showed  no  signs 
of  the  leaf  stage.  Large  plantations  of  cormels  have  been  observed  in 
which  fifty  per  cent  of  the  plants  bore  the  disease  on  the  foliage. 

Nothing  has  been  found  in  literature  that  would  indicate  that  there 
is  any  relation  between  the  leaf  stage  and  the  corm  stage  of  the  disease 
under  consideration.  It  has  been  the  writer's  fortune  to  obtain  conclusive 
evidence  that  they  are  but  different  stages  of  the  same  disease,  and  the 
experimental  data  leading  to  this  conclusion  are  here  set  forth. 

ECONOMIC    IMPORTANCE    OF    THE    DISEASE 

No  figures  are  available  to  show  the  economic  importance  of  the  hard 
rot  disease  of  the  gladiolus,  but  it  must  be  considerable  as  compared  with 
the  extent  of  the  industry.  Many  thousands  of  corms  are  discarded 
during  the  winter  and  in  the  spring  at  planting  time  because  of  their 
diseased  condition.  During  the  summer  many  thousands  of  corms  fail 
to  reach  maturity,  due  to  the  decay  of  the  parent  corms  in  the  soil.  While 
there  are  other  diseases  of  the  gladiolus,  it  is  the  opinion  of  the  writer, 
based  on  observations  made  during  the  past  four  years,  that  a  large  pro- 
portion of  this  loss  is  due  to  the  hard  rot  disease.  Several  varieties  of 
gladiolus  that  have  been  examined  showed  fifty  per  cent  or  more  of 
the  corms  to  be  affected  by  hard  rot.  So  far  as  the  writer  knows,  no 
variety  is  immune. 

While  the  loss  caused  by  the  leaf  stage  of  the  disease  is  materially  less 
than  that  caused  by  the  corm  stage,  it  is  still  of  considerable  importance 
to  the  grower.  It  has  been  observed  that  when  the  foliage  of  seedlings 
and  of  plants  from  cormels  is  affected  by  the  disease,  the  corms  are  smaller 
than  those  of  plantings  that  were  free  from  disease.  Therefore  the 
decrease  in  size  must  be  considered  along  with  the  total  loss  of  many 
thousands  of  corms.  To  this  must  be  added  the  extra  expense  incurred 
by  the  grower  in  sorting  and  selecting  more  or  less  healthy  corms  from 


156  Bulletin  380 

diseased  lots,  either  in  filling  orders  or  for  his  own  planting.     All  in  all, 
the  loss  must  take  from  the  producer  a  yearly  toll  of  surprising  magnitude. 

SYMPTOMS 

On  the  leaves 

The  first  signs  of  the  disease  on  the  leaf  are  minute  brown  or  purplish 
brown  discolored  areas  more  or  less  circular  in  outline.  These  lesions 
usually  appear  in  July  or  early  August.  The  color  of  the  diseased  areas 
deepens  somewhat  with  age  until  a  shade  from  reddish  brown  to  almost 
black  is  reached.  Spots  of  a  reddish  brown  color  predominate.  In  the 
older  lesions  there  is  a  well -differentiated  center,  light  gray  in  color  and 
dotted  with  numerous  black  bodies  which  are  very  apparent  (Plate  xv,  1). 
Surrounding  the  center  is  a  prominent  zone,  varying  from  purplish  brown 
to  black  in  color,  which  blends  into  the  green  of  the  healthy  tissue. 

The  lesions  are  more  or  less  circular  but  with  straight  sides  where 
they  are  limited  by  the  midrib  and  the  edge  of  the  leaf.  At  first  the  dis- 
coloration may  be  visible  on  only  one  side  of  the  leaf,  but  it  soon  makes  its 
appearance  on  the  opposite  side,  so  that  lesions  appear  practically  identical 
on  either  side.  They  are  few  or  numerous,  and  vary  in  size  depending 
on  conditions.  The  coalescence  of  several  or  many  spots  may  occur, 
causing  the  formation  of  a  single  large  necrotic  area  along  the  entire 
side  of  a  leaf.  Lesions  on  the  tips  of  the  leaves  are  usually  larger  and 
less  characteristic  than  those  below.  In  some  cases  the  ashen  gray  centers 
of  diseased  areas  drop  out,  giving  a  shot-hole  appearance.  This  is  more 
likely  to  occur  with  spots  on  large  flowering  plants  than  with  those  on 
seedlings. 

On  the  corms 

Hard  rot  lesions  appear  in  the  fall  as  minute  water-soaked  spots,  of 
a  reddish  brown  to  brownish  black  color,  usually  on  the  sides  and  the 
lower  half  of  the  corm  but  not  infrequently  on  the  upper  half  as  well 
(Plate  xvi).  It  is  usually  necessary  to  remove  the  husks  (sheathing  leaf 
bases)  from  the  corms  in  order  to  see  the  lesions,  although  in  some  cases 
the  husk  also  is  diseased.  The  lesion  on  the  husk  serves  as  an  indication 
of  the  more  important  lesion  underneath.  There  is  no  sharp  line  of 
demarcation  between  the  healthy  and  the  diseased  tissue. 

As  the  spot  increases  in  size,  the  center  becomes  sunken,  the  color 
deepens  to  a  distinct  black,  and  the  margin  becomes  more  definite. 
A  narrow  ring,  water-soaked  in  appearance,  still  indicates  the  advancing 
decay.  The  more  definite  margin  of  the  older  spots  is  due  to  the  rapidity 
with  which  the  sunken  condition  follows  the  advancing  water-soaked  area, 
due  to  drying  of  the  tissue.     The  tissue  gradually  becomes  hard,  in 


Bulletin  380 


Plate  XV 


HARD  ROT  LESIONS  ON  LEAVES  AND  CORMS 

1,  Lesions  on  leaves  of  gladiolus  seedlings.      X  2 

2,  Lesions  on  corms.  The  two  upper  corms  show  lesions  well  advanced,  with 
the  diseased  area  blending  into  the  healthv  tissue.  At  the  bottom  the  corm  on 
the  left  has  been  cut  in  two  in  order  to  show  the  depth  to  which  the  disease  has 
progressed.     Natural  size 


Bulletin  380 


Plate  XVI 


HARD   ROT   LESIONS   ON    CORMS 
Different  stages  in  the  destruction  of  a  corm.      X  ij 


The  Hard  Rot  Disease  of  Gladiolus  157 

some  cases  extremely  so,  making  it  difficult  to  cut  the  tissue  with  a 
sharp  knife. 

Many  small  lesions  may  coalesce  into  one  large  lesion,  in  some  cases 
leaving  areas  of  more  or  less  normal  tissue  insulated  in  a  large  sunken 
area.  Enough  tissue  not  completely  decayed  may  be  left  to  indicate 
the  margins  cf  the  formerly  separate  lesions.  Frequently  the  disease 
advances  so  far  that  the  corm  is  reduced  to  a  hard,  shriveled,  and  wrinkled 
mummy. 

Excepting  in  very  late  stages  —  and  in  some  cases  not  even  then  — ■ 
the  lesions  do  not  extend  deeply  into  the  corm.  The  usual  range  is  from 
one  to  five  or  six  millimeters  (Plate  xv,  2).  If  conditions  are  not  favor- 
able for  the  development  of  the  rot,  the  active  border  disappears,  soon 
assuming  the  sunken,  darkened  aspect  of  the  central  part.  When  this 
stage  is  reached  the  diseased  tissue  can  be  chipped  out  with  the  finger 
nail,  leaving  the  apparently  healthy  tissue  beneath,  as  if  the  disease  were 
not  now  advancing  and  the  plant  had  formed  a  callus  over  the  affected 
area. 

Plants  of  more  or  less  dwarfed,  stunted  appearance,  which  sometimes 
fail  to  produce  blossoms,  are  to  be  found  throughout  the  fields  during 
the  growing  season.  The  leaves  of  these  plants  usually  turn  brown 
and  die,  the  plant  having  the  appearance  of  having  died  from  drought. 
In  a  dry  season  the  number  of  these  plants  is  unusually  large.  At  this 
time  there  is  no  decay  of  the  new  corm  which  is  being  developed,  but 
rather  the  injury  is  caused  by  the  premature  decay  of  the  parent  corm 
before  the  offspring  has  developed  a  sufficient  root  system  to  enable 
it  to  supply  its  own  moisture  and  food,  This  premature  decay  of  the  parent 
corm  is  not  necessarily  due  to  the  advancement  of  the  hard  rot  disease, 
but  probably  in  most  cases  to  the  entrance  of  saprophytes  which  cause 
a  rapid  disintegration  of  the  corm. 


The  hard  rot  disease  of  the  gladiolus  is  caused  by  the  fungous  pathogene 
Septoria  Gladioli  Passer.  Passerini  collected  specimens  of  the  leaf  stage 
of  the  disease  on  the  foliage  of  Gladiolus  segetum  near  Parma,  Italy,  in 
June,  1874,  which  he  contributed  to  Rabenhorst's  Fungi  Europaei  — 
a  collection  of  exsiccatae  material.  On  this  packet  of  exsiccatas  material 
is  written  the  original  description  of  the  fungus.4  Passerini  noted  the 
occurrence  of  the  disease  only  on  the  leaves.     None  of  the  other  investi- 

4  Rabenhorst,  Fungi  Europaei. 
1956.     Septoria  Gladioli  Passer,  hb. 
Perithecia  punctiformia  atra  in  macula  cxarida  fulvomarginata:  sporae  cylindricae  subrectae  continuae 

hyalinae  cirrose  ejectae. 
Ad  folia  G.  segetum  Vigheffio  propc  Parmam. 
Junio  1874-  leg.  G.  Passerini. 


158 


Bulletin  380 


gators  found  a  sporulating  stage  of  the  fungus  known  to  cause  the  hard 
rot  disease  of  conns,  and  consequently  the  septorial  fungus  on  the  leaf 
was  not  associated  with  the  organism  causing  the  rot  of  the  corms. 


Life  history 
Pycnidia 

Pycnidia  (Plate  xv,  1)  of  the  hard  rot  fungus  become  visible  usually 
within  four  or  five  days  after,  or  in  some  cases  even  simultaneously  with, 
the  appearance  of  the  lesion  on  the  leaf.  They  are  imbedded  in  the  tissue, 
but  protrude  sufficiently  to  form  black  papillae  which  are  visible  to  the 
naked  eye. 

The  pycnidia  arise  from  intercellular  mycelium  (fig.  38).  They 
measure    from    100    to    160  <u    in    diameter    by    60   to    130  n    high,   the 


Fig.  38.   pycnidium  of  septoria  gladioli 

Section  through  the  pycnidium  showing  how  the  spores  are  borne.     (Outlined 
with  a  camera  lucida.)      X  3Zi 

average  being  127  n  in  diameter  by  91^  high.  The  outer  wall  of  the 
pycnidium  consists  of  pseudoparenchymatous  tissue  which  is  brown  in 
color. 

From  a  more  or  less  inconspicuous  inner  layer  of  thinner-walled  pseudo- 
parenchymatous tissue,  hyaline  conidiophores  arise.  From  these  conidio- 
phores  spores  are  cut  off  by  constriction.  In  his  description  of  the  fungus 
Allescher  (1897)  describes  the  spores  as  being  unicellular  and  measuring 
from  30  to  54  fi  long  by  2  to  2.5  ,u  in  diameter.  However,  an  examination 
made  by  the  writer  of  specimens  contained  in  packet  no.  1956  of  Raben- 
horst's  Fungi  Europaei,  as  well  as  of  fresh  material,  shows  that  the  spores 
are  usually  three-septate.  As  measured  by  the  writer  they  are  from  20  to 
55  ju.  long  by  2.25  to  4/x  in  diameter,  the  average  being  about  40  by  3  /x. 
The  spores  from  fresh  material  are  cylindrical,  almost  straight,  and  hyaline. 


The  Hard  Rot  Disease  of  Gladiolus 


i59 


When  placed  in  water  containing  small  pieces  of  leaf  tissue,  germination 
occurs  in  eighteen  hours.  From  one  to  several  germ  tubes  may  develop 
from  a  single  spore  (fig.  39). 

Mycelium 

The  mycelium  in  the  corm  is  intercellular  (figs.  40  and  41).  It  usually 
measures  from  1.5  to  2.5  /j,  in  diameter,  but  is  in  some  cases  even  double 
this  size.  The  mycelium  is  septate  and  varies  from  olive-brown  to 
black  in  color. 


Fig.  39.    spores  of  septoria  gladioli 

Some  of  the  spores  have  germinated.     (Outlined  with  a  camera  lucida.)      X  666 

Source  of  leaf  infection 

No  sexual  stage  of  the  fungus  has  been  found.  Old  leaves  bearing 
pycnidia  when  exposed  out  of  doors  throughout  the  winter  showed  usually 
only  empty  pycnidia  when  examined  the  following  spring.  From  the 
results  of  experiments  subsequently  discussed,  apparently  the  mycelium 
of  the  fungus  is  able  to  live  over  winter  in  the  soil.  This  suggests  the 
possibility  that  infection  is  produced  on  the  foliage  by  rain  splashing 
soil  containing  mycelium  on  to  the  plants,  or  by  the  plants  being  beaten 
down  on  to  the  soil  that  harbors  the  pathogene.  However,  seedlings 
around  which  rye  straw  was  placed  to  keep  them  off  the  ground  and  to 
prevent  soil  from  being  splashed  on  to  them,  were  attacked  by  the  fungus 


i6o 


Bulletin  3 So 


as  early  and  as  severely  as  those  not  so  treated;  and  attempts  to  produce 
infection  on  the  foliage  of  large  plants  by  bending  them  over  on  to  the. 


FlG.   40.      HISTOLOGICAL    EFFECT    OF   SEPTORIA    GLADIOLI 

Section  of  gladiolus  corm  through  diseased  tissue.  The  presence  of  intercellular 
mycelium,  and  the  absence  of  starch  in  many  cells,  should  be  noted.  (Compare 
with  figure  41.)       X  300 

soil  have  thus  far  failed.     Not  enough  work  has  been  done  to  either  prove 
or  disprove  these  suggested  sources  of  infection  of  the  foliage. 


FlG.   41.     MYCELIUM  OF  SEPTORIA  GLADIOLI 

The  intercellular  mycelium  is  shown  much  magnified.     (Camera  lucida  drawing.) 
X  600 


In  the  greenhouse,  the  incubation  period  of  the  fungus  on  plants 
that  were  sprayed  with  water  containing  spores  in  suspension  was  about 
twentv  davs. 


The  Hard  Rot  Disease  of  Gladiolus  161 

Source  of  corm  infection 

An  examination  of  corms  harvested  from  seed  beds  where  the  foliage 
was  badly  diseased,  has  frequently  shown  from  sixty  to  seventy  per  cent 
of  them  to  be  affected  with  hard  rot.  This,  together  with  the  fact  that 
infection  was  produced  on  corms  by  placing  in  contact  with  them  water 
containing  spores  in  suspension  (page  167),  suggests  the  probability  that 
infection  is  produced  by  spores  being  washed  down  from  pycnidia  formed 
on  the  foliage  to  the  soil,  where  they  germinate  and  infect  the  corms.  As 
seeds  are  not  planted  very  deeply,  this  could  readily  take  place.  It  is 
unusual,  however,  for  the  disease  to  appear  on  the  foliage  of  large  flowering 
plants;  and  as  pycnidia  have  not  been  observed  to  be  formed  on  the  corm, 
it  seems  that  the  fungus  is  carried  over  the  winter  primarily,  if  not  entirely, 
in  the  mycelial  stage,  no  spore  form  being  necessary  for  the  existence  of 
the  pathogene. 

The  fungus  can  be  isolated  from  lesions  on  the  corms  at  any  time  during 
winter  or  spring.  This  shows  that  the  living  organism  is  carried  to  the 
soil  along  with  the  corm  at  planting  time.  The  offspring  from  diseased 
corms  may  or  may  not  be  diseased.  As  discussed  under  control  (page  173), 
selected  healthy  conns  grown  in  soil  in  which  gladioli  have  never  been 
grown  have  without  exception  given  .sound  offspring.  This  indicates 
that  the  fungus  is  not  a  natural  inhabitant  of  the  soil.  Furthermore, 
three  hundred  corms,  all  of  which  showed  hard  rot  lesions,  were  planted 
in  soil  in  which  gladioli  had  never  been  grown,  and  seventy-eight  per 
cent  of  the  offspring  bore  hard  rot  lesions.  Thus  it  seems  that,  in  the 
majority  of  cases  at  least,  a  diseased  offspring  may  be  expected  from  the 
planting  of  a  diseased  corm. 

The  fungus  does  not  grow  directly  from  the  old  corm  into  the  new 
one.  This  has  been  determined  both  by  observations  and  by  making 
numerous  cultures  from  tissue  at  the  juncture  of  parent  and  offspring. 
The  fungus  must  either  grow  through  the  sheathing  leaf  base  from  the 
old  corm  to  the  new  one,  or  else,  as  is  probably  the  case,  grow  out  into 
the  soil,  from  which  it  attacks  the  newly  developing  corm. 

No  observations  have  been  made  which  would  lead  the  writer  to  believe 
that  all  infection  does  not  occur  in  the  field.  However,  it  is  conceivable 
that  if  corms  were  stored  under  humid  conditions  either  in  contact  with 
one  another  or  with  moist  soil,  the  fungus  might  possibly  penetrate  a 
healthy  corm  from  an  infected  one  or  from  infected  soil;  or,  if  they  were 
stored  with  soil  containing  the  pathogene  around  them,  there  is  no  doubt 
that,  under  moist  conditions,  infection  could  occur  in  the  storage  house 
as  well  as  in  the  field. 

Diseased  corms  were  minced  and  placed  in  soil  known  to  be  free  from 
the  pathogene,  in  which  two  hundred  healthy  corms  were  growing.     The 


1 62  Bulletin  380 

pieces  of  diseased  corms  were  merely  sprinkled  in  among  the  corms  before 
covering  them  with  soil  and  no  attempt  was  made  to  see  that  pieces  were 
or  were  not  in  actual  contact  with  the  healthy  corms.  Seven  per  cent 
of  the  offspring  were  diseased. 

Longevity  of  the  organism  on  the  foliage  and  in  the  soil 

As  indicated  by  the  following  experiment,  the  fungus  is  carried  over 
winter  on  diseased  tops : 

Two  hundred  corms  which  had  been  grown  for  three  consecutive  years 
in  soil  that  had  never  before  been  used  for  growing  gladioli,  were  again 
planted  in  similar  soil  in  191 5.  Previous  to  planting,  the  corms  were 
examined  and  found  to  be  absolutely  healthy.  After  setting  the  corms, 
tops  from  cormels  which  had  been  badly  affected  by  the  disease  the  pre- 
vious year  and  which  had  remained  out  of  doors  on  the  ground  throughout 
the  winter,  were  scattered  in  the  row.  The  tops  and  the  corm?  were  then 
covered  with  soil.  These  plants  were  harvested  in  September  and  the 
corms  stored  in  a  cool  place.  When  examined  early  in  December  it  was 
found  that  eighty  per  cent  of  the  corms  showed  hard  rot  lesions.  Prac- 
tically all  the  diseased  corms  had  many  lesions  on  them,  and  the  disease 
was  well  advanced.  Septoria  Gladioli  Passer,  was  isolated  from  many 
of  these  lesions,  proving  that  this  fungus  caused  the  disease.  Healthy 
corms  around  which  no  diseased  tops  were  placed  but  which  were  other- 
wise given  the  same  treatment,  showed  no  signs  of  disease. 

The  results  of  experiments  indicate  that  the  fungus  is  able  not  only 
to  live  over  winter  on  old  tops  on  the  ground,  but  also  to  live  in  the  soil 
throughout  a  period  of  at  least  four  years.  In  19 15  selected  healthy 
corms  were  planted  in  soil  in  which  gladioli  had  been  grown  the  previous 
year,  and  also  in  soil  in  which  no  gladioli  had  been  grown  for  (a)  one 
year,  (b)  two  years,  (c)  three  years,  and  (d)  four  years.  During  the 
intervening  time  the  soil  had  been  planted  respectively  to  (a)  rye  and  a 
crop  of  rye  and  vetch,  (b)  rye  and  timothy,  (c)  oats,  hay,  seeded  to  clover, 
cover  crop  of  rye  and  vetch,  (d)  grass.  In  each  of  the  five  plots  of  ground 
two  hundred  and  fifty  healthy  corms  were  planted,  two  hundred  of  them 
being  planted  in  a  single  row  and  the  remaining  fifty  in  lots  of  ten  at  five 
different  places  in  the  field.  The  corms  were  harvested  in  September  and 
stored  in  a  cool  place. 

Results  of  these  experiments  were  recorded  the  following  December. 
Forty-seven  per  cent  of  the  corms  which  were  grown  in  the  plot  in  which 
gladioli  had  been  grown  the  previous  year,  were  diseased,  fifty  per  cent 
of  the  diseased  corms  showing  characteristic  hard  rot  lesions.  The  corms 
from  the  other  plots  were  diseased  as  follows:  (a)  twenty-four  per  cent, 
forty  per  cent  of    which   bore   hard   rot    lesions;    (b)    twenty-three   per 


The  Hard  Rot  Disease  of  Gladiolus  163 

cent,  thirty-seven  per  cent  of  which  bore  hard  rot  lesions;  (c)  fifty-two 
per  cent,  eighteen  per  cent  of  which  bore  hard  rot  lesions;  (d)  forty-seven 
per  cent,  ten  per  cent  of  which  bore  hard  rot  lesions.  Care  was  taken 
during  the  summer  to  avoid  contaminating  these  plots  by  introducing 
affected  soil  from  other  fields,  and  the  location  was  such  that  it  is  extremely 
doubtful  that  the  wind  could  have  entered  as  a  factor.  Since  healthy 
corms  planted  in  soil  in  which  no  gladioli  have  been  grown  give  healthy 
offspring,  it  follows  that  the  organism  must  be  able  to  live  for  at  least 
four  years  without  the  presence  of  the  living  host.  No  doubt  decaying 
parts  of  plants  were  left  in  the  soil  when  the  last  crop  was  harvested, 
but  it  is  probable  that,  at  least  in  the  case  of  plot  d,  these  plant  parts 
were  entirely  decayed  in  the  four  years  which  intervened  between  the 
harvesting  of  the  last  crop  of  gladioli  and  the  planting  of  the  healthy 
corms  used  in  this  experiment. 

Pathogenicity 

The  pathogenicity  of  Septoria  Gladioli  Passer,  was  established  first 
for  the  mycelial  stage.  The  mycelium  of  the  fungus  was  discovered  by 
Wallace  (1909:33),  who,  after  having  observed  its  presence  in  thin 
sections  of  diseased  tissue  of  the  corm,  succeeded  in  obtaining  the  organism 
in  pure  culture.  He  later  (19 10  a)  succeeded  in  producing  the  character- 
istic lesions  on  experimentally  inoculated  corms,  and  reisolated  the  fungus. 
Following  Wallace,  Fitzpatrick  (see  footnote,  page  154)  records  having 
produced  the  characteristic  lesions  on  corms  artificially  inoculated  in 
moist  chambers,  from  which  the  fungus  was  reisolated. 

Besides  noting  the  constant  association  of  the  mycelium  with  lesions 
on  corms  through  microscopical  examinations  of  diseased  tissue,  the  writer 
has  made  numerous  isolations  of  the  organism  from  these  diseased  areas. 
The  growth  of  the  mycelium  was  studied  in  pure  culture  and  infection 
was  produced  at  will,  not  only  in  moist  chambers  in  sterile  sand,  but 
also  in  the  greenhouse,  and  in  the  field  under  natural  conditions. 

Inoculation  experiments 

Corms  were  selected  which  after  having  been  in  the  storehouse  for  four 
months  showed  no  signs  of  disease.  This  necessitated  the  removal  of  the 
husks.  The  surface  was  sterilized  by  immersing  the  corm  in  fifty-per- 
cent alcohol  for  three  minutes,  then  in  1-1000  corrosive  sublimate  solution 
for  ten  minutes,  and  finally  rinsing  in  sterile  water.  These  corms  were 
then  planted,  some  in  sterile  sand  in  moist  chambers,  some  in  soil  in  the 
greenhouse  in  which  gladioli  had  never  been  grown,  and  some  out  of 
doors  in  soil  never  before  used  for  the  growing  of  gladioli. 


j^  Bulletin  380 

For  inoculation,  mycelium  growing  in  pure  cultures  on  solid  media 
was  used.  A  bit  of  the  medium  containing  mycelium  was  removed  under 
sterile  conditions,  and  in  some  instances  smeared  over  a  part  of  the  unin- 
jured surface  of  the  corm;  in  other  cases  the  corm  was  first  injured  by 
needle  punctures  and  the  culture  was  then  smeared  on  the  surface.  The 
corms  were  permitted  to  remain  in  the  soil  for  a  period  of  two  or  three 
weeks,  when  they  were  removed  and  the  growth  they  had  made  was 
cut  off. 

In  practically  all  cases  one  hundred  per  cent  infection  was  obtained. 
Most  of  the  corms  showed  the  dark  brown,  water-soaked  areas,  char- 
acteristic of  the  hard  rot  disease,  when  dug.  The  remainder  showed  the 
lesions  very  soon  afterward.  Equally  as  abundant  infection  was  obtained 
on  the  uninjured  corms  as  on  those  punctured  by  the  needle.  From 
diseased  areas  of  the  affected  corms  the  fungus  was  reisolated  and  grown 
in  pure  culture,  where  its  growth  corresponded  in  every  detail  with  the 
organism  used  for  the  inoculation.  Corms  similarly  treated  but  having 
no  mycelium  placed  in  contact  with  them  remained  healthy  in  all  instances. 

In  order  to  further  test  the  ability  of  the  fungus  to  produce  disease, 
sound  corms  were  planted  in  soil  in  which  gladioli  had  never  been  grown, 
and  permitted  to  grow  to  maturity.  On  August  15,  19 14,  as  the  offspring 
were  developing  from  the  parent  corms,  the  soil  was  inoculated  with 
mycelium  of  the  fungus.  The  inoculum  was  prepared  by  grinding  cul- 
tures of  the  organism  on  oatmeal  agar  with  cornmeal,  and  was  applied 
by  placing  a  small  handful  of  the  mixture  around  each  corm  in  immediate 
contact  with  it.  Of  the  one  hundred  corms  thus  inoculated,  seventy-three 
showed  characteristic  hard  rot  lesions  when  the  results  of  the  experiment 
were  recorded  the  following  December.  Reisolations  of  the  fungus  were 
obtained  from  many  of  the  diseased  corms.  Corms  from  plants  which 
had  not  been  inoculated  with  mycelium  remained  absolutely  healthy. 

The  above  experiments  prove  the  ability  of  the  mycelial  stage  of  the 
hard  rot  fungus  to  attack  gladiolus  corms.  The  experiments  given  below 
show  that  this  mycelium  is  but  a  stage  of  Septoria  Gladioli,  which  Passerini 
described  as  occurring  on  the  foliage  of  Gladiolus  segetum  in  Italy. 

A  pure  culture  of  the  fungus  Septoria  Gladioli  Passer,  was  obtained 
from  the  germination  of  a  single  spore  from  a  pyenidium  formed  on  the 
leaf  of  a  gladiolus  seedling.  The  resulting  fungous  growth  was  identical 
with  that  obtained  from  isolations  from  small  pieces  of  diseased  corm 
tissue.  '  Mycelium  thus  obtained  from  a  single  spore  was  used  to  inoculate 
healthy  corms,  some  of  which  were  planted  in  moist  chambers  in  sterile 
sand,  others  in  soil  in  the  greenhouse  known  to  be  free  from  the  pathogene, 
and  still  others  out  of  doors  in  soil  in  which  gladioli  had  never  been  grown. 
Numerous  experiments  were  performed,   and  in  all  cases  one  hundred 


The  Hard  Rot  Disease  of  Gladiolus  165 

per  cent  infection  was  obtained  by  smearing  a  small  quantity  of  an  agar 
culture  of  the  mycelium  from  a  single  spore  on  the  surface  of  the  corms. 
The  fungus  was  reisolated  from  diseased  areas  on  the  corms,  and  its 
growth  in  pure  culture  was  found  to  be  identical  with  the  organism  pre- 
viously isolated  from  corms  and  from  the  germination  of  a  single 
pycnospore. 

In  order  to  test  the  ability  of  the  fungus  isolated  from  a  lesion  on  a 
corm  to  attack  the  foliage,  a  small  piece  of  an  agar  culture  of  the  organism 
was  mixed  with  a  little  sterile  distilled  water  and  painted  on  the  foliage 
of  seedlings  and  flowering  plants  growing  in  the  greenhouse.  The  seed- 
lings were  then  inclosed  in  bell  glasses  lined  with  moistened  filter  paper, 
while  the  parts  of  the  large  plants  on  which  the  mycelium  was  placed 
were  inclosed  in  a  lamp  chimney  stoppered  at  both  ends  with  cptton. 
Seedlings  and  large  plants  were  similarly  treated  with  mycelium  obtained 
from  the  germination  of  a  single  pycnospore.  Plants  were  similarly 
treated,  except  for  the  omission  of  the  mycelium,  to  serve  as  a  check. 

Inoculations  were  successful  with  both  the  mycelium  from  the  germinated 
spore  and  that  from  the  diseased  corm.  Infection  was  evident  on  the  seed- 
lings  within  ten  days.  The  lesions  differed  somewhat  from  those  found 
under  natural  conditions,  infection  manifesting  itself  in  the  form  of  large, 
dark,  water-soaked  areas,  with  the  early  death  of  the  entire  area  over 
which  the  inoculum  was  painted.  The  lesions  produced  by  mycelium 
from  the  two  different  sources  were  similar. 

On  the  large  plants,  infection  was  observed  within  fourteen  days  after 
inoculation,  the  lesions  being  identical  on  the  plants  inoculated  with 
mycelium  from  the  two  different  sources.  At  first  a  dark  area,  water- 
soaked  in  appearance,  was  formed,  and  then  the  lesions  turned  brown 
due  to  the  death  of  the  tissue.  The  lesions  in  no  case  extended  much 
farther  in  area  than  that  covered  by  the  culture  of  mycelium  painted 
on  the  foliage.  The  most  significant  fact  is  that  pycnidia  developed  in 
these  lesions  on  the  leaf  on  practically  all  of  the  twenty-four  plants  inocu- 
lated with  the  mycelium,  regardless  of  whether  the  mycelium  was  from 
a  germinated  spore  or  from  a  diseased  corm.  Although  many  pycnidia 
failed  to  reach  maturity,  spores  were  formed  in  several  of  them.  These 
spores  were  germinated  and  the  fungus  was  obtained  in  pure  culture. 

In  October,  19 14,  Septoria-like  spores  were  found  in  a  culture  of  the 
organism  isolated  from  a  diseased  corm.  These  spores,  together  with 
others  obtained  from  pycnidia  on  seedling  leaves,  were  used  in  the 
following  experiments: 

Seeds  were  planted  in  three  flats  in  the  greenhouse  and  the  plants  were 
permitted  to  grow  until  they  were  from  two  to  four  inches  high.  The 
plants  in  one  flat  were  sprayed  with  water  containing,   in  suspension, 


1 66  Bulletin  380 

spores  from  a  culture  of  the  fungus  isolated  from  a  diseased  corm;  the 
plants  in  the  second  flat  were  sprayed  with  a  suspension  of  spore's  from 
pycnidia  formed  naturally  on  seedlings;  the  plants  in  the  -remaining  flat 
were  sprayed  with  water  containing  no  spores,  for  a  check.  The  seed- 
lings were  then  covered  with  bell  glasses  lined  with  moistened  filter 
paper,  and  the  three  flats  were  placed  in  a  large  moist  propagating 
chamber  for  seventy-two  hours. 

An  examination  of  these  seedlings  twenty  days  after  they  had  been 
sprayed  with  the  suspension  of  spores  in  water  showed  evidence  of  infec- 
tion. Small  yellowish  brown  areas  were  apparent  and  numerous  pycnidia 
appeared  in  these  lesions  a  few  days  later.  The  lesions  were  characteristic 
of  those  found  on  the  seedlings  under  natural  conditions.  The  check 
plants  alone  remained  healthy,  infection  occurring  on  plants  which  were 
inoculated  either  with  spores  from  culture  or  with  spores  from  pycnidia 
formed  under  natural  conditions.  The  fungus  was  again  obtained  in 
pure  culture  from  the  germination  of  single  spores  from  pycnidia  formed 
on  both  lots  of  infected  plants. 

It  then  seemed  desirable  to  determine  whether  or  not  corms  could 
become  infected  by  spraying  spores  upon  them.  The  surfaces  of  thirty 
healthy  corms  were  sterilized  by  immersing  them  first  in  fifty-per-cent 
alcohol  for  three  minutes,  then  in  1-1000  corrosive  sublimate  solution 
for  ten  minutes,  and  finally  rinsing  in  sterile  water.  Ten  of  these  corms 
were  then  planted  in  each  of  three  moist  chambers  containing  moist  sand 
which  had  previously  been  subjected  to  steam  at  ten  pounds  pressure 
for  two  hours.  Corms  that  were  particularly  depressed  at  the  crown 
were  selected  for  the  experiment,  in  order  that  a  cubic  centimeter  or 
more  of  water  could  be  held  in  each  of  these  cavities.  Water  containing 
spores  in  suspension  was  placed  in  the  depressed  areas  of  the  corms  in 
two  of  the  moist  chambers.  The  spores  for  one  chamber  were  obtained 
from  pycnidia  formed  naturally  on  the  foliage  of  seedlings,  while  for 
the  other  chamber  the  spores  were  obtained  from  a  culture  of  the  fungus 
isolated  from  a  diseased  corm.  The  third  chamber  was  used  for  a  check, 
water  containing  no  spores  being  placed  in  the  cavities  of  the  corms. 
One-half  of  the  corms  in  each  chamber  were  then  pricked  with  a  sterile 
needle  in  the  area  covered  by  the  water. 

Observations  made  twenty  days  later  showed  most  of  the  corms  in 
the  two  chambers  which  were  inoculated  with  spores  to  be  infected.  Six 
days  later,  when  they  were  removed,  all  the  inoculated  corms  showed  the 
characteristic  hard  rot  lesions,  while  the  check  corms  remained  healthy. 
Lesions  were  as  abundant  on  corms  that  had  not  been  injured  as  on  those 
punctured  with  the  needle.  About  one-half  of  the  corms  showed  hard  rot 
lesions  on  the  sides,  where  evidently  spores  had  been  washed  over  from 


The  Hard  Rot  Disease  of  Gladiolus  167 

the  concave  crowns.    The  fungus  was  isolated  from  many  of  these  diseased 
areas  arid  again  obtained  in  pure  culture. 

In  the  spring  of  19 15  healthy  corms  were  planted  in  soil  in  which  gladioli 
had  never  been  grown,  and  allowed  to  grow  to  maturity.  On  August  2 1 
the  soil  was  removed  from  around  thirty  of  these  plants  and  water  con- 
taining a  suspension  of  spores  was  poured  around  the  corms.  At  this 
time  the  offspring  were  about  one-half  inch  in  diameter.  The  spores 
for  inoculating  fifteen  of  the  corms  were  obtained  from  pycnidia  formed 
naturally  on  the  foliage  of  seedlings,  while  for  the  other  fifteen  corms 
the  spores  were  obtained  from  a  culture  of  the  fungus  isolated  from  a 
diseased  corm.  For  a  check,  corms  were  given  the  same  treatment 
except. that  the  water  poured  around  them  contained  no  spores.  The 
soil  in  which  these  plants  were  growing  was  kept  moist  for  the  follow- 
ing three  days. 

The  corms  were  harvested  in  the  following  September  and  stored  in  a  cool 
place.  When  examined  in  November  it  was  found  that  ten  of  the  fifteen 
corms  inoculated  with  spores  from  pycnidia  showed  hard  rot  lesions; 
also,  six  of  the  fifteen  corms  inoculated  with  spores  from  culture  showed 
lesions  characteristic  of  the  hard  rot  disease.  The  check  plants  remained 
healthy.  This  experiment  is  significant  in  showing  not  only  that  spores 
from  cultures  and  from  naturally  formed  pycnidia  are  able  to  infect  the 
corms,  but  also  that  it  is  possible  for  infection  to  occur  on  the  corms  from 
spores  discharged  from 
pycnidia  on  the  leaves. 
The  spores  are  washed 
down  into  the  soil, 
where  they  germinate 
and  produce  infection. 


Pathological  histology 

Leaf 

An    examination  of 
thin  sections  of  leaves 

«  •  -,•  „     j  FlG.   42.       HISTOLOGICAL  EFFECT  OF  SEPTORIA  GLADIOLI 

bearing  young  diseased      *       ^ .    ,     ,     „  ,_    L    .      ,   • 

0  J  .  Camera  lucida  drawing  of  a  free-hand  section  through  a  hard  rot  lesion 

areas  shoWS  the   lesion   on  the  leaf  of  a  seedling.    The  cells  are  beginning  to  shrivel  and  collapse. 

produced  by  the  fun- 
gus to  be  necrotic.  The  cells  turn  brown,  shrivel,  and  collapse  (fig.  42). 
Here  and  there  a  cell  may  be  found  filled  with  a  yellow,  granular  or 
oil-like  substance  the  identity  of  which  is  undetermined.  The  diseased 
area  is  usually  but  from  one-third  to  one-half  the  thickness  of  the 
healthy  tissue. 


1 68 


Bulletin  380 


Corm 

In  order  to  study  the  histological  changes  that  occur  in  the  corm,  com- 
parative studies  of  healthy  and  diseased  tissues  have  been  made.  Both 
microtome  and  free-hand  sections  have  been  used,  the  former  being  less 
satisfactory  because  of  the  difficulty  encountered  in  sectioning  prepared 
material.  Sections  were  stained  with  a  weak  solution  of  iodine  in  order 
to  study  starch  content  of  cells,  and  with  Haidenheim's  iron-alum-hasma- 
toxylin  and  aniline  blue  for  a  general  study  of  the  tissue. 

While  the  cells  of  healthy  tissue  are  densely  packed  with  starch,  those 
of  diseased  tissue  show  but  very  few  starch  grains  or  none  at  all  (figs.  40 
and  41  [page  160],  and  43).  This,  together  with  the  deposit  in  the 
diseased  area  of  a  yellow  substance  of  undetermined  composition,  is  the 

most  pronounced  effect  to 
be  noticed  by  comparing 
sections  of  diseased  and 
healthy  tissue.  Espe- 
cially in  the  early  stages 
of  the  disease,  nuclei  and 
even  the  cytoplasm 
appear  but  slightly  dis- 
turbed. The  cell  walls 
retain  their  shape  for 
some  time  after  the  starch 
has  disappeared.  Later, 
shrinkage  takes  place  and 
the  cells  collapse,  the 
walls  becoming  distorted 
and  broken.  This  last 
rather   than    to    any   direct 


HISTOLOGICAL    EFFECT   OF  SEPTORIA  GLADIOLI 


Camera  lucida  drawing  of  a  microtome  section  through  medium 
of  healthy  and  diseased  tissue.  The  layer  of  comparatively  thin- 
walled  cork  cambial  cells  separating  the  starch-filled  healthy  cells 
from  the  diseased  cells,  which  contain  little  or  no  starch,  should 
be  noted.      X  300 


effect  is  no  doubt  due  to  loss  of  moisture 
action  of  the  fungus. 

A  layer  of  cork  cambium  is  formed  at  the  juncture  of  the  diseased 
and  the  healthy  tissue  (fig.  43).  Young,  actively  advancing  lesions  do 
not  show  this  layer  of  thin-walled  cells,  but  it  is  to  be  found  in  those 
instances  in  which  it  appears  that  the  advance  of  the  disease  has  been 
checked  and  the  canker  healed.  In  cases  in  which  the  diseased  area 
can  be  chipped  out,  the  break  is  at  this  layer  of  cork  cells. 

Cultural  characters  of  the  fungus 

Pure  cultures  of  Septoria  Gladioli  Passer,  were  obtained  from  isolation 
plantings  of  diseased  tissue  from  a  corm.  The  surfaces  of  corms  showing 
hard  rot  lesions  were  disinfected  by  immersing  them  in  fifty-per-cent 
alcohol  for  three  minutes,  then  in  1-1000  corrosive  sublimate  solution 


The  HAkD  Rot  Disease  of  Gladiolus 


169 


for  ten  minutes,  and  finally  rinsing  in  sterile  water.  By  means  of  a  sterile 
scalpel  the  surface  of  the  corm  was  cut  away  and  a  small  piece  of  the 
tissue  at  the  advancing  margin  of  the  lesion  was  removed  to  a  sterile 
medium.  Comparatively  few  contaminations  were  obtained  in  the  large 
number  of  isolations  made  in  this  manner. 

No  marked  difference  was  observed  in  the  growth  of  the  mycelium 
on  nutrient  or  on  soil-extract  agar,  or  on  other  solid  media  consisting  of 
agar  and  various  plant  decoctions,  such  as  of  gladiolus,  potato,  oats,  corn, 
and  beans.  On  the 
other  hand,  rolled-oat 
agar5  proved  slightly 
more  favorable  for 
mycelial  growth,  and 
spores  were  produced 
by  the  fungus  only 
when  growing  on  this 
medium.  For  this 
reason  rolled-oat 
agar  was  used  almost 
entirely  for  culturing 
the  organism  during 
the  last  year  of  study, 
and  the  following  cul- 
tural characters  of 
the  fungus  are  a  rec- 
ord of  its  growth  on 
this  medium. 

Macroscopically, 
no  growth  from  bits 
of  diseased  tissue 
placed  in  medium  in 
previously 

petri  dishes  is  evident 
for  from  seven  to  fourteen  days.  However,  if  the  plate  is  examined  under 
the  low  power  of  the  microscope,  mycelium  radiating  from  the  transferred 
piece  of  tissue  can  be  seen  in  about  four  or  five  days  from  the  time  of 
making  the  culture.  Frequently  the  first  macroscopical  evidence  of  growth 
is  the  appearance  of  a  black  growth  on  the  transferred  piece  of  tissue, 
which    may  be   completely   covered   before   the  organism    invades  the 

5The  rolled-oat  agar  was  prepared  as  follows:  50  grams  of  rolled  oats,  in  700  cubic  centimeters  of  dis- 
tilled water,  was  cooked  in  a  double  boiler  for  about  an  hour,  or  until  the  oats  were  thoroughly  cooked 
through.  Most  of  the  solid  matter  was  then  squeezed  through  cheesecloth.  To  this  was  added  15  grams 
of  agar  and  enough  water  to  make  one  liter  of  medium. 


MYCELIUM    OF    SEPTORIA    GLADIOLI 


Camera  lucida  drawing  of  mycelium  of    the  hard  rot  fungus  growing 
on  rolled-oat  agar.     A,  colorless  strands  of  hyphte  radiating  from  a  bit 
of  diseased  tissue.     B  and  D,  cell  walls    that    have    thickened,  the  cells 
DOUrcd     having  assumed  a  globose  form.     C,  colorless    hyphffi  to  be  found  in  old 
cultures.     E,  an  intermediate  stage  between  A  and  B.      X  600 


i7o  Bulletin  380 

medium.  Soon  a  dense,  black  colony  spreads  very  slowly  into  the  sur- 
rounding medium.  After  growth  of  a  month  the  colonies  usually  do  not 
exceed  one  or  two  centimeters  in  diameter.  If  portions  of  a  colony  are 
transferred  to  flasks  of  media  or  to  other  plates,  the  resulting  growth  is 
somewhat  more  rapid. 

Some  of  the  characters  of  the  mycelium  as  grown  in  culture  are  shown 
in  figure  44.  The  first  strands  of  hyphas  to  be  seen  radiating  from  the 
piece  of  diseased  tissue  are  hyaline  (fig.  44,  a).  Color  frequently  makes 
its  appearance  in  streaks,  which  radiate  from  the  piece  of  diseased  corm, 
whsre  the  hyphae  seem  to  become  gnarled.  Cells  of  the  much-septate 
mycelium  thicken,  assuming  a  globose  form  (fig.  44,  b).  Well-defined 
globular  bodies,  which  appear  to  be  oil  drops,  soon  appear  within  the 
cells.  Osmic  acid  causes  these  to  turn  brown.  The  walls  turn  brown 
with  the  appearance  of  these  bodies,  giving  the  colony  its  black  color 
when  viewed  macroscopically.  The  globose  or  subglobose  cells  of  the 
hyphas  may  remain  attached,  forming  chains,  or  may  separate  into 
individual  cells  (fig.  44,  b). 

Although  the  growth  is  usually  confined  beneath  the  surface  of  the 
medium,  small  scant  patches  of  white,  aerial  mycelium  are  found  occa- 
sionally. The  hyphas  of  old  cultures  is  of  two  kinds:  one  of  compara- 
tively long,  colorless  cells  measuring  from  1.5  to  about  4  [x  in  diameter 
(fig.  44,  c,  e);  and  one  of  short,  thick,  globose  cells  containing  the  oil 
drops  mentioned  above,  measuring  from  3  to  6  or  7  ju,  or  sometimes  even 
12  fx,  in  diameter  (fig.  44,  b,  d). 

Scattered  through  the  colonies  are  areas  which  under  the  microscope 
appear  denser  and  blacker  than  other  areas.  These  seem  to  be  caused 
by  a  gnarling,  or  balling,  of  the  hyphae  at  these  points,  together  with 
the  anastomosing  of  cells  of  different  hyphas,  as  if  pycnidia  or  other 
fruit  bodies  were  to  be  formed.  Cultures  have  been  examined  inter- 
mittently throughout  a  period  of  over  three  years,  and  no  further  develop- 
ment of  these  masses  of  hyphas  has  been  observed. 

Spores  of  Septoria  Gladioli  Passer,  were  first  observed  in  culture  in 
October,  19 14.  The  mycelium  on  which  these  spores  were  formed  was 
isolated  in  the  preceding  June,  from  a  hard  rot  lesion  on  a  corm.  This 
mycelium  was  allowed  to  grow  in  a  tube  of  rolled-oat  agar  from  June 
until  August  20,  when  a  square  block  of  the  medium  containing  mycelium 
was  transferred  to  the  slanted  surface  of  about  200  centimeters  of  rolled- 
oat  agar  contained  in  a  300-cubic-centimeter  Erlenmeyer  flask.  The 
medium  contained  in  this  flask  was  freshly  prepared.  There  were  about 
10  cubic  centimeters  of  water  of  condensation  in  the  flask  at  the  base  of 
the  slanted  medium.  The  culture  from  which  the  transfer  was  made  was 
well  dried  at  the  time  when  the  square  of  medium  containing  mycelium 


The  Hard  Rot  Disease  of  Gladiolus  171 

was  removed,  and  this  condition  may  have  influenced  spore  formation 
when  the  mycelium  was  placed  on  the  freshly  prepared  medium. 

By  approximating  the  above  conditions  the  writer  has  been  able  to 
bring  about  the  formation  of  spores  in  cultures  of  the  mycelium  from 
other  sources  than  the  one  above  noted.  Spores  were  formed  in  a  culture 
of  the  mycelium  obtained  from  the  germination  of  a  single  pycnospore 
formed  naturally  on  the  leaf.  Spores  formed  in  cultures  of  mycelium 
isolated  from  corms  and  from  germinated  pycnospores  were  identical 
in  shape  and  sizs,  thus  materially  helping  to  establish  the  identity  of 
the  two  previously  unconnected  organisms: 

Spores  in  culture  have  always  appeared  as  minute  pinkish  white  pustules 
on  the  upper  edge  of  the  block  of  medium  containing  mycelium  trans- 
ferred from  the  old  culture.  Later  these  pustules  may  appear  scattered 
over  the  surface  of  the  medium  of  the  flask  to  which  the  transfer  was 
made.  If  at  this  time  transfers  are  made  from  this  flask  to  another,  the 
pustules  are  formed  more  readily  and  in  greater  abundance. 

Owing  to  difficulties  encountered  in  obtaining  sections  or  mounts  of 
these  pinkish  white  elevations,  but  little  is  known  of  their  structure, 
especially  in  reference  to  the  formation  of  the  spores.  Normal  pycnidia 
such  as  those  formed  on  the  foliage  are  not  produced.  The  spores  are 
formed  in  a  very  loose  stromatic  mass.  There  is  an  abundance  of  dense, 
pinkish  white  mycelium,  which  is  still  in  evidence  after  spores  are  no 
longer  to  be  found  associated  with  the  pustules. 

Spores  formed  in  culture  are  variable  in  size,  ranging  from  25  to  97  m 
by  1.8  to  3.75  n,  the  average  being  58  by  2.71  /*.  Dilution  plates  of  these 
spores  were  made  in  nutrient  agar  and  practically  one  hundred  per  cent 
germination  was  obtained  within  a  period  of  eighteen  hours.  The  result- 
ing mycelial  growth  was  not  so  brown  in  color  as  that  isolated  from  corms. 
Many  minute,  black  dots  appeared,  which,  when  examined  under  the 
microscope,  proved  to  be  aggregations  of  short,  thick-walled  cells  formed 
commonly  and  more  abundantly  in  cultures  of  the  fungus  isolated  from 
corms.  Transfers  were  made  from  these  plates  to  tubes  of  rolled-oat 
agar,  where  the  resulting  growth  was  identical  with  that  obtained  by 
isolations  made  from  diseased  corms. 

In  order  to  correlate  the  growth  of  mycelium  isolated  from  diseased 
tissue  of  corms  with  that  isolated  from  the  leaf,  dilution  plates  of  spores 
from  naturally  formed  pycnidia  were  made.  From  these  dilution  plates 
individual  spores,  which  were  so  located  that  they  could  be  removed 
singly,  were  transferred  to  other  plates  where  germination  was  observed 
under  the  microscope.  The  resulting  mycelial  growth  in  all  cases  has 
been  identical  with  that  isolated  from  corms  when  the  two  were  growing 
under  similar  conditions. 


172  Bulletin  380 

CONTROL 

The  great  need  of  some  method  of  combating  the  organisms  causing 
rots  of  gladiolus  corms  was  early  impressed  upon  the  writer,  and  many 
suggested  methods  of  general  application  were  tried  for  the  control  of 
the  rots  collectively  rather  than  separately.  Another  disease,  designated 
by  Wallace  (1909:61)  as  dry  rot,  was  found  to  be  present  along  with 
the  hard  rot  disease  in  stock  which  was  used  in  all  control  experiments. 
The  lesions  produced  by  the  fungi  causing  these  two  diseases  are  so  similar 
that  they  can  be  distinguished  only  in  the  earliest  stages,  and  not  even 
then  with  a  great  degree  of  accuracy.  Cultural  isolations  of  the  organisms 
will  often  show  a  lesion  to  have  been  caused  by  the  hard  rot  fungus  when 
it  was  selected  as  being  a  dry  rot  lesion,  or  vice  versa.  Not  only  are  the 
lesions  produced  by  the  two  fungi  similar,  but  the  life  histories  of  the 
organisms  are  not  materially  unlike  except  for  the  fact  that  no  spore 
form  of  the  dry  rot  fungus  has  been  found.  From  all  indications,  a  treat- 
ment applicable  to  the  control  of  one  disease  should  be  of  value  in  con- 
trolling the  other.  At  least  fifty  per  cent  of  the  corms  used  for  experimental 
purposes  were  affected  with  the  hard  rot  disease.  This  estimate  is  based 
on  observations  and  cultural  studies  throughout  a  period  of  several  years. 
In  practically  all  cases,  after  the  corms  were  treated,  the  organisms  have 
been  isolated  from  diseased  areas  in  order  to  make  it  absolutely  certain  that 
both  were  present,  and  in  no  case  has  any  treatment  resulted,  so  far  as 
the  writer  was  able  to  judge,  in  materially  changing  the  ratio  of  the  corms 
affected  by  the  two  diseases. 

In  view  of  the  fact  that  control  experiments  were  conducted  previous 
to,  and  simultaneously  with,  life  history  studies,  it  is  not  surprising  that 
some  treatments  which  at  first  seemed  worthy  of  trial  failed  to  bring 
results.  Many  of  the  following  treatments  have  given  negative  results. 
This  does  not  wholly  deprive  them  of  their  value,  for  they  serve  to  narrow 
down  the  field  of  experimental  possibilities  of  control.  Many  data  have 
been  obtained  from  the  treatments  which  will  be  valuable  in  a  further 
study  of  control    measures. 

SEEDLING    TREATMENTS 

The  hard  rot  disease  on  the  foliage  of  seedlings  has  been  materially 
reduced  by  spraying  with  bordeaux  mixture  used  at  the  strength  of  five 
pounds  of  copper  sulfate  and  five  pounds  of  lime  to  fifty  gallons  of  water. 
In  19 14  the  first  spray  was  applied  on  July  17.  This  application  was 
followed  by  eight  other  treatments  made  at  intervals  of  about  seven  days. 
Because  of  the  smooth  surface  of  the  foliage,  it  was  necessary  to  use  a 
"sticker,"  or  adhesive,  to  cause  the  fungicide  to  adhere  to  the  plants. 
The  "  sticker  "  used  consisted  of  resin  two  pounds,  sal  soda  (crystals) 


The  Hard  Rot  Disease  of  Gladiolus  173 

one  pound,  and  water  one  gallon,  which,  after  being  boiled  until  a  clear 
brown  color  was  obtained,  was  added  to  each  fifty  gallons  of  the  bordeaux 
solution.  The  seedling  beds  were  sprayed  twice  the  same  day  for  each 
application,  the  second  spray  being  applied  as  soon  as  the  first  was  dried 
on  the  foliage.  This  was  done  in  order  to  thoroughly  cover  the  plants. 
A  hand  sprayer  was  used,  in  which  a  pressure  of  from  three  and  one-half 
to  five  pounds  could  be  maintained  at  all  times. 

H.  H.  Groff,  of  Simcoe,  Ontario,  informed  the  writer  that  he  was 
successful  in  controlling  a  disease  of  the  foliage  of  seedlings  by  spraying 
with  a  solution  of  copper  sulfate  in  water.  Specimens  of  the  disease  sent 
by  Mr.  Groff  to  the  writer  proved  to  be  the  hard  rot  disease.  From  the 
nature  of  the  foliage  of  the  gladiolus,  it  is  probable  that  the  plant  is  more 
resistant  to  spray  injury  than  are  most  plants  and  that  a  solution  of  copper 
sulfate  could  be  used  without  causing  injury.  However,  no  experiments 
have  been  conducted  by  the  writer  using  copper  sulfate  solution  as  a  spray 
for  the  control  of  this  disease,  and  it  is  very  unlikely  that  results  could  be 
obtained,  because  the  copper  sulfate  would  be  washed  away  with  the 
first  rain. 

Although  spraying  will  greatly  reduce  the  amount  of  disease  on  the 
foliage,  a  simpler  and  more  efficient  method  is  to  plant  the  seed  in  soil  in 
which  gladioli  have  never  been  grown.  When  this  was  done,  and  care 
was  taken  not  to  carry  parts  of  diseased  plants  or  soil  bearing  the  fungus 
to  these  seedlings,  it  was  found  that  not  a  single  diseased  plant  appeared 
during  the  summer.  The  corms  of  these  plants  were  materially  larger  when 
harvested  than  the  corms  of  plants  whose  foliage  was  attacked  by  the 
hard  rot  fungus,  and  no  evidences  of  disease  on  the  corms  were  observed. 
This  is  the  logical  way  to  control  the  hard  rot  disease,  which  causes  so  much 
damage  in  seedling  beds.  It  is  doubtful  whether  any  grower  plants 
such  a  large  quantity  of  seed,  or  has  such  a  limited  area  of  ground,  that 
soil  in  which  gladioli  have  never  been  grown  cannot  be  obtained  for  this 
purpose.  If  this  plot  is  kept  isolated  and  care  is  taken  not  to  introduce 
the  pathogene  into  the  soil,  there  appears  to  be  no  reason  why  seedlings 
cannot  be  grown  on  the  same  area  year  after  year,  if  necessary,  at  least 
so  far  as  the  hard  rot  disease  is  concerned. 

CORM    TREATMENTS 

Healthy  corms  in  soil  free  from  the  pathogenes 

Selected  healthy  corms  have  been  grown  for  the  past  four  years  in 
soil  in  which  no  gladioli  had  ever  before  been  planted,  without  a  single 
corm's  becoming  diseased.  The  fact  that  these  corms  were  stored  through- 
out each  winter  in  a  room  containing  diseased  corms  leads  to  the  con- 


174  Bulletin  380 

elusion  that  the  fungi  causing  the  hard  rot  and  dry  rot  diseases  are  not 
disseminated  in  storage.  It  is  obvious  that  in  order  to  obtain  results  from 
the  selection  of  healthy  corms,  rigid  and  painstaking  care  must  be  exercised 
to  select  corms  known  to  be  absolutely  free  from  disease.  Any  doubtfully 
healthy  corms  must  be  rejected,  for  a  single  diseased  corm  may  serve  to 
infect  the  soil  in  which  healthy  corms  are  planted. 

To  select  healthy  corms  it  is  necessary  to  remove  the  husks  and  to  be 
sure  there  is  no  evidence  of  disease  on  the  corms.  It  is  best  to  do  the 
selecting  in  the  spring,  as  near  planting  time  as  possible,  for,  whereas 
a  corm  may  be  infected  in  the  fall  at  digging  time  and  still  show  no  evidence 
of  being  diseased,  the  lesion  is  sure  to  be  noticeable  by  planting  time. 
Previously  to  planting  these  corms  it  is  advisable  to  treat  them  with 
a  five-per-cent  solution  of  formalin  for  thirty  minutes,  in  order  to  kill 
any  parts  of  the  pathogenes  which  may  be  clinging  to  them. 

In  191 2  from  two  thousand  to  three  thousand  healthy  corms  were  selected 
in  the  manner  suggested  above.  They  were  planted  each  year  in  soil 
that  had  not  been  under  cultivation  for  about  twenty  years.  A  com- 
mercial phosphate  fertilizer  was  applied  to  the  experimental  plots  at  the 
rate  of  about  five  hundred  pounds  to  the  acre,  and  the  corms  were  planted 
in  the  usual  manner.  Care  was  exercised  to  see  that  no  foreign  soil  nor 
diseased  plant  parts  were  introduced  into  these  plots.  The  plants  received 
the  usual  amount  of  cultivation  and  were  subjected  to  the  same  con- 
ditions as  commercially  grown  plants.  Spikes  of  flowers  were  cut  during 
the  blooming  season,  and  the  corms  were  harvested  and  stored  each 
autumn  in  the  ordinary  way. 

This  process  of  selecting  healthy  corms  and  growing  them  in  soil  free 
of  the  pathogenes  is  the  only  means  known  that  will  give  an  absolutely 
healthy  crop.  Of  course  the  large  amount  of  labor,  the  carelessness  of 
laborers,  the  need  of  a  larger  outlay  of  land,  and  the  inability  to  procure 
land  on  which  gladioli  have  never  been  grown  or  at  least  not  for  many 
years,  are  some  of  the  important  factors  that  will  at  once  suggest  themselves 
to  growers,  especially  the  larger  growers  who  produce  many  thousands 
of  corms  annually.  It  is  admitted  that  this  is  a  slow  and  somewhat 
undesirable  method  from  many  standpoints,  yet  it  is  a  process  that  has 
proved  conducive  to  results,  and  undoubtedly  can  find  some  application 
by  all  growers.  Small  growers  can  readily  and  with  no  great  loss  adopt 
such  a  method  for  growing  gladioli.  Larger  growers  can  adopt  the  process 
in  part. 

Such  a  method  could  be  begun  on  a  small  scale,  by  selecting  as  many 
healthy  corms  the  first  year  as  conveniently  possible  and  planting  them 
in  soil  in  which  gladioli  had  never  been  grown.  More  selected  corms 
could  be  added  to  this  lot  the  second  year,  and  so  on  until  the  grower 


The  Hard  Rot  Disease  of  Gladiolus  175 

gradually  worked  away  from  diseased  to  healthy  stock.  The  opportunity 
for  healthy  corms  to  become  diseased  is  thus  lessened,  and  diseased  con- 
ditions are  in  general  improved. 

Healthy  corms  in  soil  known  to  harbor  the  pathogenes 

When  selected  healthy  corms  were  planted  in  soil  in  which  gladioli 
had  been  grown  the  previous  year,  the  offspring  were  diseased.  The 
amount. of  disease  varied  from  twenty- three  to  forty-seven  per  cent. 
The  possibility  suggested  itself  that  some  treatment  might  be  devised 
which  would  protect  the  offspring  of  the  sound  corms  that  were  planted, 
from  the  pathogenes  that  must  be  in  the  soil. 

An  experiment  was  conducted  in  19 14  in  which  the  corms  of  the  various 
plots  were  treated  with  different  chemicals.  A  small  handful  of  the 
chemicals  was  placed  over  each  corm  previously  to  covering  the  corms 
with  soil.  The  chemicals  used  were:  plot  1,  sulfur;  plot  2,  air-slaked 
lime;  plot  3,  acid  phosphate;  plot  4,  soot.  The  soot  was  suggested  by 
a  grower  who  claimed  to  have  obtained  good  results  through  a  liberal 
application  of  this  substance  to  the  soil.  The  plants  received  ordinary 
cultivation  during  the  summer,  and  the  offspring  were  harvested  and  stored 
in  the  usual  manner.  In  December,  when  the  results  of  the  experiments 
were  recorded,  it  was  found  that  none  of  the  treatments  were  of  any  value, 
the  percentages  of  disease  in  the  treated  plots  being  practically-  the  same 
as  that  in  a  check  plot  where  no  treatment  was  given.  The  experiment 
was  repeated  in  191 5  with  the  same  results. 

Diseased  corms  in  soil  free  from  the  pathogenes 

Spring  treatments 

When  diseased  corms  that  had  received  no  treatment  were  planted  in 
soil  free  from  the  pathogenes,  it  was  found  that  the  offspring  gave  various 
percentages  of  disease.  Seventy-eight  per  cent  „of  the  offspring  from 
three  hundred  corms  bearing  typical  hard  rot  lesions,  which  were  planted 
in  soil  free  from  the  pathogenes,  were  diseased.  In  other  instances,  thirty- 
three  and  fifty-seven  per  cent  diseased  offspring,  respectively,  were  recorded 
from  the  planting  of  two  lots  of  three  hundred  corms  affected  with  either 
hard  rot  or  dry  rot,  or  both. 

An  experiment  was  conducted  in  1914  to  determine  whether  or  not 
some  treatment  could  be  given  these  corms  at  planting  time  which  would 
lessen  the  amount  of  disease  in  the  offspring  when  the  corms  were  grown 
in  soil  free  from  the  pathogenes.  Corms  that  bore  typical  hard  rot  lesions, 
and  others  that  were  affected  with  either  the  hard  or  the  dry  rot  disease 
or  both,  received  the  following  treatments:   (1)  formalin  at  the  rate  of 


176  Bulletin  380 

one  pint  of  commercial  formalin  to  fifteen  gallons  of  water,  for  eighteen 
hours;  (2)  corrosive  sublimate,  1-1000  solution,  for  eighteen  hours; 
(3)  chemicals,  in  which  the  corms  were  rolled  and  with  which  they  were 
covered  after  being  placed  in  the  rows  and  before  covering  them  with 
soil.  The  chemicals  used  were  sulfur,  air-slaked  lime,  acid  phosphate, 
and  soot.  The  corms  were  planted  in  soil  in  which  gladioli  had  never 
bsfore  been  grown,  and  received  ordinary  cultivation  during  the  summer. 
When  the  corms  were  examined  in  December,  1914,  the  results  obtained 
indicated  that  none  of  the  treatments  were  effective  in  reducing  the 
amount  of  disease.  The  experiment  was  repeated  in  1915,  with  the 
same  results  except  that  corms  over  which  a  handful  of  sulfur  was  placed 
were  injured  severely  by  the  chemical.  Such  treatments  of  diseased 
corms  have  proved  to  be  of  no  value  in  controlling  the  hard  rot  and  dry 
rot  diseases. 

Autumn  treatments 

Since  the  lesions  on  corms  attacked  by  the  hard  rot  and  dry  rot  organisms 
are  materially  smaller  in  the  autumn  when  the  corms  are  dug  than  in  the 
winter,  it  was  thought  that  possibly  the  corms  could  be  given  some  treat- 
ment at  digging  time  whereby  the  pathogenes  within  the  tissues  would 
be  killed.  Consequently  the  following  experiments  were  performed 
with  the  hope  of  at  least  lessening  the  extent  of  injury  to  the  corms. 

Experiment  1.  Treatment  of  corms  with  formalin  and  corrosive  sublimate 
solutions. —  In  1914  one  thousand  corms,  of  which  many  had  lesions 
in  various  stages  of  advancement  at  digging  time,  were  treated, 
immediately  after  digging,  with  formalin  at  the  strength  of  one  pint  of 
commercial  formalin  to  fifteen  gallons  of  water,  in  which  they  were  left 
for  eighteen  hours.  An  equal  number  of  corms  were  treated  with  1-1000 
corrosive  sublimate  solution  for  eighteen  hours,  and  an  equal  number 
were  left  untreated  for  a  check.  After  treatment  the  conns  were  cured 
out  of  doors  and  then  stored  as  usual. 

In  the  following  December,  when  the  results  of  these  treatments  were 
recorded,  it  was  found  that  neither  had  reduced  the  amount  or  the  extent 
of  the  diseases.  Thirty-five  per  cent  of  the  offspring  from  the  untreated 
corms  were  diseased,  while  thirty-seven  and  thirty-eight  per  cent, 
respectively,  of  the  offspring  from  the  corms  treated  with  formalin  and 
corrosive  sublimate  solution  were  diseased. 

The  same  experiment  had  been  performed  the  previous  season  (19 13), 
with  the  result  that  about  ninety  per  cent  of  the  corms  of  both  the  treated 
lots  were  diseased  while  the  corms  in  the  check  were  but  seventy  per 
cent  diseased.  This  remarkable  situation  is  difficult  to  explain.  There 
was  a  prolonged  period  of  wet  weather  about  the  time  the  treatments 


The  Hard  Rot  Disease  of  Gladiolus  177 

were  made,  so  that  the  corms  remained  wet  for  about  a  week  after  they 
were  treated.  The  corms  were  either  injured  by  being  subjected  to  the 
action  of  the  reagents  for  so  long  a  time,  or  else  the  increased  per- 
centage of  diseased  corms  was  due  to  some  other  abnormal  condition 
brought  about  by  the  wet  condition  of  the  corms.  Many  of  the  corms 
bore  lesions  which  were  not  characteristic  of  either  the  hard  rot  or  the  dry 
rot  disease,  from  which  neither  the  dry  rot  organism  nor  Septoria  Gladioli 
Passer,  could  be  isolated. 

Experiment  2.  Formaldehyde  gas  as  a  disinfectant. —  On  the  basis  of 
successful  experiments  performed  for  the  control  of  potato  scab  by  the 
use  of  formaldehyde  gas,  diseased  corms  were  subjected  in  19 13  to  a 
similar  treatment.  Obviously  this  would  eliminate  the  humid  condition 
arising  from  the  use  of  solutions. 

In  this  experiment  the  gas  was  generated  by  the  potassium  permanganate 
method.  At  harvesting  time  one  thousand  corms  were  placed,  immediately 
after  digging,  in  shallow  trays  in  a  large  air-tight  box.  The  formaldehyde 
gas  was  obtained  by  using  enough  potassium  permanganate  to  generate 
gas  at  the  rate  of  three  pints  of  formalin  and  twenty-three  ounces  of 
permanganate  crystals  to  five  hundred  cubic  feet  of  space,  it  having 
been  previously  determined  that  corms  thus  treated  were  unharmed. 
The  treatment  extended  over  a  period  of  twenty-four  hours.  The  corms 
were  then  thoroughly  cured  in  the  open  air  and  stored  as  usual. 

In  January,  19 14,  when  the  results  of  this  treatment  were  recorded, 
it  was  found  that  sixty-nine  per  cent  of  the  corms  were  diseased  while 
seventy  per  cent  of  the  untreated  corms  from  the  same  lot  were  diseased. 
The  hard  rot  and  dry  rot  organisms  were  isolated  from  many  lesions, 
showing  both  organisms  to  be  alive.  The  difference  of  one  per  cent  in  the 
amount  of  disease  can  easily  be  explained  on  the  basis  of  experimental 
error,  with  the  resulting  conclusion  that  formaldehyde  gas  as  used  in 
this  experiment  is  of  no  value  in  controlling  the  corm  rots  of  gladioli. 

Experiment  3.  Hot-water  and  hot-air  treatments  of  diseased  corms. —  In  a 
third  experiment  some  means  was  sought  whereby  diseased  corms  could 
be  subjected  to  heat,  which  would  kill  the  organisms  within  the  tissue 
without  causing  injury  to  the  corms.  After  such  treatment  the  corms 
could  be  planted  in  soil  known  to  be  free  of  the  pathogenes  and  be  depended 
on  to  yield  a  healthy  crop. 

Previously  to  conducting  the  experiments  it  was  determined  that 
the  thermal  death  point  of  the  hard  rot  and  dry  rot  organisms  was  about 
500  C.  when  subjected  to  this  temperature  in  a  test  tube  culture  for 
a  period  of  ten  minutes.  The  tubes  were  immersed  in  the  hot  water  as 
soon  as  new  growth  appeared  from  pieces  of  medium  containing  mycelium 
which  were  transferred  to  the  tubes.     It  was  also  previously  determined 


178  Bulletin  380 

that  corms  of  from  three-fourths  inch  to  one  and  one-half  inches  in 
diameter,  when  subjected  to  dry  heat  at  500  C.  for  one  and  one-half  hours 
or  to  water  at  this  temperature  for  one-half  hour,  were  not  materially 
harmed. 

Having  thus  obtained  some  idea  of  the  relative  resistance  of  both 
corms  and  the  two  pathogenes  to  heat,  corms  were  subjected  in  19 13 
to  dry  heat  and  to  water  at  500  C.  for  one  and  one-half  hours  and  one-half 
hour,  respectively,  and  the  progress  of  the  disease  was  noted.  There 
was  enough  difference  between  the  length  of  time  required  to  kill  the 
fungi  and  that  which  caused  no  injury  to  the  corms  to  warrant  this  treat- 
ment. The  corms  used  were  of  a  single  variety  and  showed  considerable 
disease  when  dug.  They  were  treated  on  the  same  day  that  they  were 
harvested.  For  the  hot-water  treatment  a  half-bushel  galvanized  iron 
measure  was  used,  the  heat  being  supplied  by  an  oil-stove  flame,  and  for 
the  dry-air  heating  a  Freas  electric  oven  was  used.  After  treatment 
the  corms  were  cured  as  quickly  as  possible  and  then  stored  in  a  cool 
place  as  usual.  Wet  weather  lengthened  the  time  necessary  to  thoroughly 
cure  the  corms  more  than  was  desirable. 

In  the  following  January,  when  the  results  of  this  experiment  were 
recorded,  it  was  found  that  seventy  per  cent  of  the  untreated  corms 
bore  lesions  of  either  the  hard  rot  or  the  dry  rot  disease,  while  of  those 
treated  with  dry  heat  and  hot  water  eighty-five  and  ninety-five  per  cent, 
respectively,  were  diseased.  In  both  cases  in  which  treatments  were 
given,  the  corms,  besides  containing  a  large  percentage  of  disease,  showed 
the  lesions  to  be  more  advanced  than  those  in  the  check.  Both  the 
hard  rot  and  dry  rot  organisms  were  isolated  from  many  diseased  corms 
of  both  lots,  showing  the  pathogenes  to  be  still  alive. 

In  accounting  for  the  increased  percentages  of  disease  in  the  treated 
over  the  untreated  corms,  it  was  found  that  many  of  the  lesions,  besides 
being  different  in  appearance  from  those  produced  by  the  two  fungi, 
were  identical  with  those  produced  on  healthy  corms  which  were  sub- 
jected to  heat  under  the  same  conditions  and  from  which  neither  the 
hard  rot  nor  the  dry  rot  organism  could  be  isolated.  These  lesions  were 
undoubtedly  due  to  injury  caused  by  the  heat.  However,  a  sufficiently 
large  number  of  corms  bore  characteristic  lesions  of  the  two  diseases, 
and  the  causal  organisms  were  isolated  from  enough  lesions,  to  prove  that 
the  treatments  were  a  failure  in  killing  the  fungi  within  the  tissue  at  a 
temperature  that  would  not  injure  the  corm. 

SOIL   TREATMENTS 

Experiment  1.  Chemicals. —  Since  the  organisms  causing  the  hard  rot 
and  dry  rot  diseases  are  able  to  live  over  winter  in  the  soil,  the  possibility 


The  Hard  Rot  Disease  of  Gladiolus  179 

suggested  itself  that  some  chemical  might  be  applied  to  the  soil  which, 
either  through  its  toxicity  or  by  its  ability  to  change  the  composition 
of  the  soil  thereby  rendering  it  unsuited  for  the  existence  of  the  pathogenes, 
would  serve  to  eradicate  them.  Healthy  eorms  could  then  be  planted 
safely  in  this  soil. 

For  the  experiment  in  1912  a  plot  of  land  was  used  on  which  gladioli 
had  been  grown  for  the  past  three  years.  The  chemicals  used  and  the 
amounts  per  acre  were  as  follows:  air-slaked  lime,  1200  pounds;  sulfur, 
1000  pounds;  air-slaked  lime  800  pounds,  and  sulfur  1000  pounds;  sulfate 
of  iron,  1800  pounds;  acid  phosphate,  1200  pounds;  acid  phosphate,  2100 
pounds.  The  chemicals  were  applied  by  the  use  of  a  lime  spreader, 
in  strips  of  10  by  136  feet,  a  strip  of  equal  width  being  left  between  each 
of  the  treated  areas  to  serve  as  a  check.  The  entire  experiment  was 
conducted  in  triplicate.  Across  the  strips  and  at  right  angles  to  them 
were  planted  the  rows  of  corms,  each  row  consisting  of  a  single  variety. 
During  the  growing  season  special  care  was  taken  to  see  that  no  soil 
was  carried  from  one  treated  area  into  another  or  into  the  checks.  The 
results  of  the  treatments  were  based  on  corms  removed  from  a  center 
seven-feet  strip  of  each  of  the  treated  and  the  check  areas. 

In  the  following  January,  when  the  results  of  this  experiment  were 
recorded,  it  was  found  that  none  of  the  treatments  had  been  of  any  value. 
No  reduction  whatever  was  obtained  in  the  amount  of  disease  in  treated 
as  compared  with  untreated  corms.  Since  the  chemicals  were  applied 
in  as  large  amounts  as  is  commercially  practicable,  if  not  larger,  no 
further  soil  treatments  with  chemicals  have  been  tried  on  a  large  scale. 

Experiment  2.  Formalin  as  a  soil  disinfectant. —  Soil  in  which  seedlings 
had  been  grown  for  the  past  two  years  was  treated  in  191 2  with  one  gallon 
of  one-per-cent  formalin  solution  per  square  foot.  The  plot  was  covered 
with  heavy  burlap  for  two  days  after  being  treated.  As  soon  as  the 
odor  of  formaldehyde  could  no  longer  be  detected,  seeds  were  planted 
in  the  treated  soil,  other  seeds  being  planted  in  untreated  soil  to  serve 
as  a  check. 

During  the  summer  the  hard  rot  disease  appeared  on  the  foliage  of 
these  seedlings.  No  doubt  infection  occurred  from  spores  blown  from 
diseased  seedlings  growing  near  by  in  untreated  soil.  The  corms  were 
harvested  in  the  autumn  and  stored  in  a  cool  room. 

In  the  following  January,  when  the  corms  were  examined,  it  was  found 
that  seventeen  per  cent  of  those  grown  in  treated  soil  were  diseased,  while 
thirty-seven  per  cent  of  the  corms  from  untreated  soil  showed  disease. 
Since  the  disease  appeared  on  the  foliage  of  these  plants  during  the  summer, 
it  was  impossible  to  determine  whether  the  source  of  infection  was  the 
mycelium  of  the  fungus  in  the  soil,  or  spores  that  might  have  been  washed 


180  Bulletin  380 

down  from  the  leaves  to  the  soil  where  they  would  germinate  and  infect 
the  corms.  Therefore  it  was  impossible  to  determine  from  this  experiment 
whether  or  not  the  formalin  treatment  had  been  of  value  as  a  soil  dis- 
infectant. The  experiment  was  repeated  in  191 5,  but  no  results  were 
obtained  because  the  seed  planted  failed  to  germinate. 

Experiment  j.  Formalin  as  a  soil  disinfectant. —  The  value  of  formalin 
as  a  soil  disinfectant  for  Septoria  Gladioli  Passer,  and  the  dry  rot  fungus 
was  further  tested  by  treating  soil  in  which  gladioli  had  been  grown  for 
the  past  two  years  with  formalin  at  the  rate  of  one  gallon  of  one-per-cent 
solution  per  square  foot.  Healthy  corms  were  planted  in  this  soil.  No 
lesions  of  the  hard  rot  disease  appeared  on  the  foliage  during  the  summer. 
In  the  following  January,  when  the  corms  were  examined,  it  was  found 
that  the  treatment  had  proved  of  no  value  in  reducing  the  percentage 
of  disease,  as  compared  with  healthy  corms  growing  in  untreated  soil. 
However,  the  treated  plat  was  not  sufficiently  isolated  from  other  untreated 
areas  to  preclude  the  possibility  that  infected  soil  might  have  been  carried 
from  untreated  soil  to  that  which  was  treated,  and  hence  the  results 
must  be  considered  with  that  restriction. 

SANITATION 

It  has  been  shown  that  the  hard  rot  fungus  is  able  to  live  over  winter 
on  dead  tops  left  lying  about  on  the  ground.  It  follows  that  these  tops 
should  be  raked  up  in  the  fall  and  burned.  This  suggestion  applies 
particularly  to  the  tops  of  seedlings  and  cormels,  since  the  disease  has 
been  observed  by  the  writer  to  occur  on  the  foliage  of  but  six  plants 
of  flowering  size.  It  has  also  been  indicated  that  the  fungi  causing  the 
hard  rot  and  dry  rot  diseases  of  gladioli  will  live  in  the  soil  for  at  least 
four  years.  Care  should  therefore  be  taken  that  the  soil  does  not  become 
infected  with  the  pathogenes.  Only  healthy  corms  should  be  planted 
in  soil  which  it  is  desired  to  keep  free  from  these  fungi;  at  least  more 
care  should  be  exercised  at  planting  time  to  see  that  no  corms  badly 
diseased  are  planted.  Such  corms  should  be  discarded  and  burned, 
for  they  will  but  decay  in  the  soil  and  infect  it  with  the  disease-producing 
organisms.     Crop  rotation  should  be  practiced. 

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